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(SAN) proponents. Some believe that Fibre Channel SANs are faster; others that that an iSCSI storage infrastructure is cheaper.

But these generalizations do not capture the complexities of the debate. Fibre Channel SANs enjoy their own connective fabric and a more optimized protocol stack, for example. But iSCSI storage infrastructures can ride on top of an existing Ethernet investment, and link aggregation can be easier than with Fibre Channel configurations.

The widespread embrace of virtualization, along with its overall cost reductions, has now brought the iSCSI-vs.-Fibre Channel debate to the smallest environments. Regardless, one of virtualization's major philosophical questions remains the same: Which storage infrastructure is a better fit?

Is the extra infrastructure investment for Fibre Channel's fully separate fabric worth the performance improvements? Even though iSCSI can run atop an existing Ethernet network, will it result in poor performance or lax security? Which storage infrastructure will net the best performance, greatest scalability and most flexibility?

A January 2009 Forrester Research report surveyed 124 global clients about enterprise storage decisions -- more specifically: What drives a SAN purchase? It appears that virtualization isn't the answer.

As reported in the survey and analyzed in chapter three of the Data Center Servers and Storage e-book, 89% of respondents did not build a SAN because of a virtual environment implementation, and only 7% built a SAN for virtualization purposes and continued to use that SAN for virtualization -only uses.

So, what does this mean? In the end, what storage will you use for your virtual machines? In all likelihood, the storage will be the storage you've already got, as I noted in my e-book.

Choosing iSCSI or Fibre Channel storage infrastructure Obviously, this realization means little to an organization that doesn't have a SAN. But if your business has deployed a virtual environment and is considering a SAN, which type should you choose?

In most real-world scenarios, the performance difference between Fibre Channel and iSCSI SANs is negligible. Partisans will extol the raw performance statistics of their favorite SAN type, but it's fantastically difficult to translate raw performance specifications into real-world user experience.

Other decisions in your environment's design tend to define baseline performance long before raw SAN metrics come into play. Server-to-storage connections over iSCSI or Fibre Channel can be aggregated in various ways to make their differences insignificant. Overall, Fibre Channel disks tend to have a marginal performance advantage, but disk rotation speeds between the two SAN types are generally similar.

Performance alone may not be a decisive factor, but a SAN's ease of administration can be. The management tools and techniques for Fibre Channel and iSCSI storage infrastructures are substantially different.

For some time, Fibre Channel SANs, fwent without universal vendor agreements for management protocols, driver sets and even terminology. As a result, two SAN vendors probably won't share management approaches. Additionally, the skills and experience required to run a Fibre Channel storage infrastructure are difficult to come by -- often requiring additional consulting support for most implementations to start correctly.

On the other hand, iSCSI SANs lean heavily on the existing TCP/IP protocol. If you have network engineers in your environment, they probably possess most of the necessary skills to successfully manage an iSCSI storage infrastructure.

When implementing an iSCSI storage infrastructure, however, be wary of a vendor's claim that it can piggyback on an existing Ethernet investment. ISCSI SANs can run atop traditional network equipment, but virtualization storage traffic traverses a network at a much greater volume than regular network traffic. So even if your existing network can handle the load, network performance may suffer. Your network may require additional investments, such as more powerful equipment, to achieve the performance you need.

In the end, it's a toss-up between Fibre Channel and iSCSI storage infrastructures. The decision should occur after looking through your provider's price sheet and assembling a return on investment assessment.

Greg Shields is an independent author, instructor, Microsoft MVP and IT consultant based in Denver. He is a co-founder of Concentrated Technology LLC and has nearly 15 years of experience in IT architecture and enterprise administration. Shields specializes in Microsoft administration, systems management and monitoring, and virtualization. He is the author of several books, including Windows Server 2008: What's New/What's Changed, available from Sapien Press.

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